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[newbie] Define and use records in sum types
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Date: -- (:)
From: Markus Mottl <mottl@m...>
Subject: Re: [newbie] Define and use records in sum types
On Wed, 19 Jul 2000, John Gerard Malecki wrote:
> Many of the professional programmers I show ocaml to like it very much
> but are annoyed by this behavior.  Maybe there is a reasonable work
> around?  The normal solution for the behavior of ocaml records is to
> prepend the record name to the field name.  For example,
> 
> 	type male = { male_name : string; male_salary : int }
> 	type female = { female_name : string; female_salary : float }

Ahem, do you want to express with this example that women earn so little in
your company as compared to men that you need floats to express their
salary? ;-)  (only joking!)

Well, anyway, modules solve the problem quite well - why not use them?  The
effort is hardly worth mentioning.

E.g.:

  module Male = struct
    type t = { name : string; salary : int }
    let raise_salary p n = { p with salary = p.salary + n }
  end

  module Female = struct
    type t = { name : string; salary : float }
    let raise_salary p n = { p with salary = p.salary +. n }
  end

  let _ =
    let male = { Male.name = "Albert"; Male.salary = 1000 }
    and female = { Female.name = "Berta"; Female.salary = 1000.0 } in
    let happy_male = Male.raise_salary male 100
    and happy_female = Female.raise_salary female 100.0
    and other_female = { female with Female.name = "Caroline" } in
    ()

> but then reference
> 
> 	 { male:salary = x }

The module version nearly looks the same ("." instead of ":" and capital
letter). Additionally, it forces people to introduce some modularity into
the program, which is hardly a drawback.

> The idea is to allow the disambiguation to be optional.  It may
> confuse novices but ...

I'd opt against this: to me, modules already provide a regular way to
organize namespaces - no need to add even further constructs to the
language...

Best regards,
Markus Mottl

-- 
Markus Mottl, mottl@miss.wu-wien.ac.at, http://miss.wu-wien.ac.at/~mottl